Paleomagnetism of the Todos Santos and La Silla Formations, Chiapas: Implications for the opening of the Gulf of Mexico Antonio Godínez-Urban1, Roberto S. Molina Garza2, John W. Geissman3, and Tim Wawrzyniec3 1Posgrado en Ciencias de la Tierra, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, 76100, Mexico 2Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, 76100, Mexico 3Department of Earth and Planetary Sciences, MSC 03 2040, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, USA ABSTRACT an Euler rotation pole for the Maya Block 1992) as well as the tectonic grain in the deep for this time period in the eastern gulf. The Gulf of Mexico (Scott and Peel, 2001). The We report paleomagnetic data for the apparent polar wander path defi ned by granitoids of the Chiapas Massif record west- Lower to Middle Jurassic La Silla and Todos paleomagnetic poles for the Chiapas Massif directed characteristic magnetizations that yield Santos formations of southern Mexico, in and Jurassic rocks reported here suggests a paleomagnetic pole position in the central west-central Chiapas and the Tehuantepec that relative motion between North America equatorial Pacifi c. These data have been inter- Isthmus region. Volcanic rocks and red beds and the Maya Block occurred between Late preted to refl ect large magnitude counterclock- of these formations were deposited prior to Permian and Early Jurassic time, during a wise rotation of the Maya Block with respect to or during the early stages of Gulf of Mexico protracted rifting phase, and then in the Late North America (Molina-Garza et al., 1992). The opening. Dual-polarity characteristic mag- Jurassic in association with seafl oor forma- rotation indicated by paleomagnetic data for the netizations reside primarily in hematite and tion in the Gulf. Chiapas Massif, however, is larger (~70°) than pass intraformational conglomerate, regional suggested in plate reconstructions (35° –55°). tilt, and reversal tests; they are thus inter- INTRODUCTION AND The basement structure of the western Gulf preted as primary magnetizations. Our sam- PREVIOUS WORK of Mexico is thought to be dominated by attenu- pling sites are concentrated in three locali- ated crust whose primary features were defi ned ties; around La Angostura Lake, 17 accepted It is generally accepted that the Gulf of by the south-southeast drift of the Maya Block sites yield a tilt corrected mean of declination Mexico formed by counterclockwise rotation along the eastern margin of Mexico (Buffl er, (Dec) = 325°, inclination (Inc) = 4.6° (k = 11.9, of the Maya (or Yucatán) Block in the Late 1983; Buffl er and Sawyer, 1985; Ewing, 1991; α 95 = 10.8°); in the Matías Romero region, Jurassic following a protracted episode of con- Marton and Buffl er, 1994; Wawrzyniec et al., the mean is Dec = 312.9°, Inc = 3.2° (based tinental rifting that initiated in the Late Triassic 2003; Wawrzyniec et al., 2004; Ambrose et al., on only seven sites); and in the Custepec (Pindell and Dewey, 1982; Hall et al., 1982; 2003). This is supported by a steep north-south– area, Jurassic andesitic dikes intruding rocks Pindell, 1985; Buffl er and Sawyer, 1985; Pin- trending basement step and associated geo- of the Permian Chiapas Massif yield a cor- dell et al., 2006). Independent motion of the physical anomalies, including a coast-parallel rected mean of Dec = 335.0°, Inc = 5.0° (six Maya Block with respect to both North and magnetic maximum and a steep gravity gradient sites). The mean directions are discordant South America is supported by the development offshore of the Mexican states of Tamaulipas and with respect to expected North America ref- of rift basins as well as Upper Jurassic passive Veracruz. These anomalies appear to follow the erence directions, and indicate a counter- margin sequences surrounding it. The inferred trace of the Tamaulipas-Golden Lane-Chiapas clockwise rotation of 35° to 40°. Inclinations timing of counterclockwise rotation in the Late transform (Pindell, 1985), a structure considered indicate deposition or emplacement at near Jurassic is constrained by (1) plate kinematics to have accommodated rotation of the Maya equatorial paleolatitudes (2.1°N ± 3.4°). This (Pindell and Dewey, 1982; Pindell et al., 1988; Block. It also has been proposed that the Maya paleolatitude estimate is statistically indis- Bird et al., 2005; Pindell et al., 2006); (2) the Block was rotated about an Euler pole in the tinguishable from those previously observed Jurassic stratigraphy of the Gulf and northeast eastern Gulf region, located near the southern in the La Boca Formation of the Huizachal Mexico (e.g., Winker and Buffl er, 1988; Salva- Florida peninsula or western Cuba (e.g., Pindell Group in northeast Mexico. The localities we dor, 1987; Goldhammer, 1999), as it is gener- and Dewey, 1982; Hall and Najmuddin, 1984; sampled in southern Mexico are separated by ally assumed that rotation of Yucatán post-dates Marton and Buffl er, 1994; Pindell et al., 2006). ~150 km, suggesting that the paleomagnetic Callovian salt deposition; (3) isotopic (190.4 ± Because of uncertainty in the magnitude of signature of these rocks refl ects regional- 3.4 Ma) age determinations of rift-related dia- rotation, several details in the reconstruction scale rather than local deformation. These base dikes offshore of Yucatan (Schlager et al., of the Maya Block in the northern Gulf region Jurassic paleomagnetic directions support 1984); and (4) paleomagnetic data for the San remain unsolved, as illustrated in Figure 1. For a rotational origin for the Gulf of Mexico. Ricardo Formation along the northeast fl ank example, Ross and Scotese (1988) reconstruct The data are also consistent with an Early to of the Chiapas Massif (Guerrero-García et al., the Maya Block farther west than other mod- Middle Jurassic reconstruction that places 1990). The rotation of the Maya Block itself is els. Pindell and Kennan (2009), on the other the Chiapas Massif offshore the Tamauli- supported by paleomagnetic results for the Late hand, propose a tighter fi t, and the Maya Block pas state in the western Gulf of Mexico, and Permian Chiapas Massif (Molina-Garza et al., is placed farther north than other models, while Geosphere; February 2011; v. 7; no. 1; p. 145–158; doi: 10.1130/GES00604.1; 8 fi gures; 3 tables. For permission to copy, contact [email protected] 145 © 2011 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/7/1/145/3339426/145.pdf by guest on 29 September 2021 Godínez-Urban et al. Dickinson and Lawton (2001) locate the Maya 180 Ma Block farther east than other models. Similarly, the orientation of the rift structures in continen- tal lithosphere that facilitated opening of the Gulf is uncertain, and somewhat controversial (Pindell et al., 2006; Exxon, 1985; Salvador, 1987). Some authors have suggested that rela- tive motion between the Chiapas Massif and the Maya Block occurred during the rifting process or at a later time (e.g., Ross and Scotese, 1988; Dickinson and Lawton, 2001). Therefore paleo- magnetic data of Permian age from the Permian Ross and Scotese, 1988 Massif may not refl ect with suffi cient accuracy the rotation of the Maya Block during opening Tr-J of the Gulf of Mexico. Furthermore, plutonic rocks lack reference to paleohorizontal, and, in the absence of robust fi eld relations involving overlying stratifi ed rocks, paleomagnetic data from them are inherently of lower reliability than those from stratifi ed rocks. The limited paleo- magnetic data for the Todos Santos Formation ? reported by Molina-Garza et al. (1992) suggest that Jurassic rotation of the Maya Block is closer ? to the 35° –45° estimate that has been recently proposed in several paleogeographic reconstruc- Dickinson and Lawton, 2001 tions (e.g., Mickus et al., 2009; Pindell et al., 2006), but the overall quality of that Todos San- tos paleomagnetic data set from the Tehuantepec 190 Ma region is inadequate for a reliable reconstruction. The paleopole for the Chiapas Massif, and the larger rotation inferred by Molina-Garza et al. (1992), may thus refl ect internal deformation of - the Maya Block during the rifting phase of conti- nental breakup, or other tectonic processes such as Neogene deformation. Other paleomagnetic data suggest a more complex scenario for Mesozoic deformation (Steiner, 2005). Paleomagnetic data from the Santa Rosa Group in the Maya Mountains have been interpreted by Steiner (2005) to indicate Pindell and Kennan, 2009 ~180° of rotation of the Maya Block since the mid-Permian. In essence, paleomagnetic data 165 Ma from the Maya Mountains are similar to results from the Chiapas Massif. In the Maya Moun- tains, early Paleozoic intrusions that have been affected by a late Paleozoic thermotectonic event and yield Permian–Triassic K-Ar dates yield a paleomagnetic pole in the equatorial Pacifi c near the pole for the Chiapas Massif. Mid-Permian sedimentary rocks of the Santa Rosa Formation yield shallow, south-southwest magnetizations defi ning a pole at 62.5°N/22.6°E. The Santa Rosa Formation paleopole for the Maya Mountains is at an angular distance of 27° ± 17° from the pole reported for the upper Paleozoic sequence from Bird and Burke, 2006 the Chicomuselo uplift in Chiapas (the pole is located at 74.2°N–95.4°E; Gose and Sánchez- Figure 1. Selected reconstructions of western equatorial Pangea, with emphasis on the posi- Barreda, 1981). Both poles fall near the Juras- tion of the Yucatan block. Modifi ed after Ross and Scotese (1988), Dickinson and Lawton sic segment of the North American apparent (2001), and Pindell and Kennan (2009). polar wander path. Molina-Garza et al. (1992) 146 Geosphere, February 2011 Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/7/1/145/3339426/145.pdf by guest on 29 September 2021 Paleomagnetism of Todos Santos and La Silla formations reported similar, shallow and south-directed, deposited in alluvial fan, fl uvial, and lacustrine of the Todos Santos Formation and the under- magnetizations for Todos Santos strata in the environments (Blair, 1987).